I have a Dell XPS15 1970 laptop, with nVidia GeForce GTX 1050 Ti graphics card.
I have a second monitor connected directly to the computer with an HDMI cable.
When I boot the computer with Ubuntu 20.04, the external monitor works great, no problems. When I boot with Windows 10, the display settings detect the external monitor (i.e., it shows 2 displays in the display window, I can move the cursor or windows onto the second monitor), but the actual monitor displays only a black screen (when I restart the monitor, it says "No signal" before showing the black screen).
The problem persists when I switch to different HDMI cables or to other external monitors. All the other questions I found on this same issue seem to boil down to "change the cable", but since Ubuntu handles the same monitor with the same cable, it doesn't feel like a hardware problem. Or if it is, what is Ubuntu doing that allows it to overcome the hardware problem?
I've had this problem for about 2 years. The windows partition used to handle external monitors without any problems.
Following a different trouble-shooting thread, I tried disabling the Intel graphics driver and restarting. After this, Windows could not detect the second monitor at all. After re-enabling the Intel driver, it detected the monitor again but still showed only a black screen.